1. Field of the Invention
The present invention relates to a heating apparatus, and more particularly, to a heating apparatus using an electromagnetic wave. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for increasing a capacity of a cavity and for enhancing cut-off performance of the electromagnetic wave.
2. Discussion of the Related Art
Generally, an electronic oven, a microwave oven and the like are devices for heating food and drink using an electromagnetic wave. And, a heating apparatus using an electromagnetic wave is the general term for theses devices.
A heating apparatus using an electromagnetic wave according to a related art includes a choke filter provided to an edge of a door to prevent the electromagnetic wave from leaking through a gap between an open front side of a body and the door. And, the front side of the body and the choke filter configure an electromagnetic wave cut-off circuit (L-C circuit).
And, the door of the electronic oven is configured to be projected to a prescribed height inward the cavity for thermal insulation of a high temperature state within the cavity. Namely, the door is configured to have a thin edge.
A gasket and a glass panel is provided to the door of the heating apparatus using the electromagnetic wave for air-tightness and thermal insulation of the inside of the cavity.
The heating apparatus using the electromagnetic wave heats food and drink in a manner of applying the electromagnetic wave having a frequency of about 2.45 GHz suitable for heating the food and drink well to the inside of the cavity.
However, the related art heating apparatus using the electromagnetic wave has the following problems.
First of all, since the gasket and glass panel are installed at the door of the heating apparatus for the thermal insulation, a gap between the front side of the body and the choke filter is unable to avoid increasing. If the gap increases, capacitance (C) of the electromagnetic wave cut-off performance is reduced so that a graph, as shown in FIG. 1, has a sharp peak to considerably reduce an electromagnetic wave absorption bandwidth having the cut-off performance below about 70 dB. Hence, the electromagnetic wave cut-off performance is considerably lowered.
As the gap between the front side and the choke filter increases, the electromagnetic wave absorption bandwidth sensitively varies in a direction of being narrowed. For instance, if a gap between the front side of the body and a coil, as shown in FIG. 1, is 1 mm (G1), the electromagnetic wave absorption bandwidth is about 100 MHz. If the gap between the front side of the body and the coil, as shown in FIG. 1, is 3 mm (G2), the electromagnetic wave absorption bandwidth is about 50 MHz. If the gap between the front side of the body and the coil, as shown in FIG. 1, is 10 mm (G3), there exists almost no electromagnetic wave absorption bandwidth. Yet, in case that the gasket and the glass panel are installed at the door of the heating apparatus, a substantial gap between the front side of the door and the choke filter is about 6˜7 mm, it can be seen that the electromagnetic wave cut-off performance is considerably reduced.
Secondly, the cavity has the EMI (electromagnetic interference) characteristic since the electromagnetic wave interference or electromagnetic interference (EMI) is generated by a harmonic frequency due to the interference of the frequency of 2.45 GHz. As the electromagnetic wave bandwidth is reduced, it becomes difficult to eliminate the harmonic frequency.
Thirdly, the volume (size) of the cavity attempts to be increased in a manner of reducing a wall thickness of the body to increase a capacity of the electronic or microwave oven. Once the thickness of the front side of the body is decreased, an area of the front side of the body is decreased so that the capacitance (C) is considerably reduced to decrease the electromagnetic wave cut-off circuit considerably. Thus, limitation is put on reducing the wall thickness of the body.